1. Art Field
The present invention relates generally to a fabrication system for fabricating an organic electroluminescent (hereinafter called organic EL for short) display device, and more specifically to a fabrication system for storing the substrate to be provided with a film, forming an organic material-containing thin film on the substrate and storing the substrate with the thin film formed thereon, and an organic EL display device fabrication process using the system.
2. Background Art
An organic EL display device comprises a matrix or other array of organic EL elements wherein light emitting elements are selectively driven to arrange characters, etc., thereby displaying information thereon. Basically, an organic EL element is built up of a tin-doped indium oxide (ITO) or other transparent hole injecting electrode (anode), a thin film form of a hole transporting material such as tetraphenyldiamine (TPD) formed as by vapor deposition on the transparent electrode, an organic light emitting layer formed of a fluorescent material such as an aluminoquinolinol complex (Alq3) and laminated on the thin film, and an electron injecting electrode (cathode) provided on the organic light emitting layer and formed of a material having a low work function, for instance, Mg. This element now attracts attention because a luminance as high as several hundred to tens of thousands cd/m.sup.2 is achievable at an applied voltage of approximately 10 V. To arrange organic EL elements an a matrix or other form, for instance, JP-A 5-275172 discloses that an anode is provided on a transparent substrate, and then patterned, after which a structure rendering patterning on a cathode side possible is formed by photolithography. JP-A 5-275172 also teaches a method for forming this cathode isolation structure with a negative or positive photoresist.
In many cases, an inter-layer insulating film is provided on the anode, as set forth in JP-A's 3-250583 and 3-274694. JP-A 3-250583 discloses that the inter-layer insulating film is formed of polyimide while JP-A 3-274694 discloses a method for forming the inter-layer insulating film using a photoresist.
Thus, organic materials such as photoresists and polyimides are usually deposited on an organic EL display device substrate.
On the other hand, an organic EL display device is very sensitive to moisture. For instance, moisture has adverse influences on the organic EL display device, offering problems such as a separation between the light emitting layer and the electrode layer, and degradation of the constituting materials, which may other cause dark spots and so make it impossible to maintain light emission.
A substrate with an organic structure provided thereon adsorbs much moisture in the atmosphere. When such a substrate is immediately charged in a vacuum film formation chamber, it is required to evacuate a vacuum tank over a long period of time so as to reduce the remaining moisture therein to a sufficiently low level and then initiate film formation. It is thus required to operate a vacuum deposition system for an extended period of time, resulting in an increase in the fabrication cost of organic EL display devices.
In the fabrication process of an organic EL display device, the treatment of a substrate with films formed thereon is very important for the reason of having a close relation to the service life thereof. Usually, the substrate with films formed thereon is sealed up, as disclosed in JP-A 5-89959. When the substrate is sealed up after delivered out of a vacuum atmosphere into the atmosphere, however, it is affected by atmospheric moisture, resulting in the occurrence of display defects such as dark spots, and disadvantages such as loss of service life. With a continuous film formation system wherein substrates with films formed thereon are stored in the atmosphere as often found in a film formation system for liquid crystals, a storage time difference between substrates poses a problem in connection with the quality stability of the display device to be fabricated.
Referring here to a fabrication process of a substrate having such a structure as a cathode isolation structure or an inter-layer insulating film structure, the remnants of organic structures such as photoresists and polyimides are likely to be left on the cathode, too. When an organic EL display device is formed on a anode contaminated with the remnants, display defects such as luminance variations and dark spots are caused together with a driving voltage rise, resulting in disadvantages such as loss of service life.
For removal of atmospheric organic matters and dust deposited onto the anode, JP-A 9-232075 discloses a method of irradiating the anode with ultraviolet rays or ion beams in a vacuum tank. Only by use of irradiation with ultraviolet radiation, and ion beams, however, it is impossible to provide sufficient removal of photoresists or polyimides firmly deposited onto the anode in the substrate fabrication process. Another problem with the method set forth in JP-A 9-232075 is that some considerable expense is added to the system cost and the system running cost. Removal of organic materials may also be achieved by cleaning with ozone gas generated under reduced pressure from an ozonizer. However, it is again impossible to provide effective removal of photoresists or polyimides firmly deposited onto the anode during the substrate fabrication process.
It is therefore an object of the invention to provide a system and process for fabricating an organic EL display device with high yet stable quality and at low cost.